Objective: The role of coronary collateral circulation (CCC) on the improvement of left ventricular function in coronary artery disease is controversial. The aim of this study is to investigate the effect of CCC on left ventricular function in patients with ischaemic heart disease. Methods: Accordingly, 76 patients (39 female, 37 male, mean age - 61±17 years) who had single vessel disease with >85% narrowing in left anterior descending coronary artery were enrolled in this study. Coronary collateral circulation was determined according to the Rentrop classification (Class 0= no collateral circulation; class 1= small branches of occluded vessel fill with CCC; class 2= epicardial segment of the occluded vessel partially fills with CCC; class 3= epicardial segment of the occluded vessel totally fills with CCC). Left ventricular function was assessed with echocardiography and left ventricular regional wall motion score (0=normokinetic; 1= hypokinetic; 2= akinetic; 3= dyskinetic; 4= aneurysmatic). Rentrop classification of the patients were compared with left ventricular regional wall motion scores and ejection fractions. Results: Twenty one of 76 patients had no collateral circulation. The regional wall motion score of class 0 patients was similar with that of patients with CCC (class 1,2,3) (2.28 ± 2.1 vs 3.39 ± 2.1, p>0.05). Particularly, the regional wall motion score was positively correlated with Rentrop classes (p<0.05). Class 3 patients had the highest wall motion score (4.24 ± 2.5, p<0.05). Patients with and without CCC had similar left ventricular ejection fractions (49±11 vs 46± 17, p>0.05). Conclusion: This study showed that development of CCC has no preventive effect on left ventricular functions in patients with coronary artery disease. Interestingly as the stage of CCC increases left ventricular function worsens. It may be the result of the fact that patients with well developed CCC have more severe coronary artery disease.